Method, system and components for facilitating wireless communication in a sectored service area

ABSTRACT

A access point (AP) during wireless communication with at least one wireless transmit/receive unit (WTRU), transmits a beacon signal periodically among a plurality of sectors, each sector having its own sector identity, the beacon signal being periodically received at least once in a beacon period and the beacon period comprising a plurality of beacon service periods for all sectors. The AP determines a scheduling value to indicate a number of inactive beacon periods for a first sector to at least one WTRU located in the first sector. The scheduling value is transmitted with the sector identity for the first sector, such that a variable beacon period is established for the first sector, enabling the at least one WTRU located in the first sector to enter a sleep mode for an adjustable period of time.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/787,392, filed Apr. 16, 2007, which is a continuation of U.S. patentapplication Ser. No. 11/023,861, filed Dec. 28, 2004 which issued asU.S. Pat. No. 7,206,610 on Apr. 17, 2007, which claims the benefit ofU.S. Provisional Patent Application No. 60/622,900, filed Oct. 28, 2004,which are incorporated by reference as if fully set forth.

FIELD OF INVENTION

The present invention relates to a wireless communication system. Moreparticularly, the present invention relates to wireless local areanetworks (WLANs), such as IEEE 802.11 networks, and to a communicationmethod and components, such as access points (APs) that use beamforming, which provide communication services to a region for wirelesstransmit/receive units (WTRUs).

BACKGROUND

Wireless communication systems are well known in the art. Generally,such systems comprise communication stations, which transmit and receivewireless communication signals between each other. Depending upon thetype of system, communication stations typically are one of two types ofwireless transmit/receive units (WTRUs): one type is the base station,the other is the subscriber unit, which may be mobile.

The term base station as used herein includes, but is not limited to, abase station, access point, Node B, site controller, or otherinterfacing device or WTRU in a wireless environment, that providesother WTRUs with wireless access to a network with which the AP isassociated.

The term wireless transmit/receive units (WTRU) as used herein includes,but is not limited to, a user equipment, mobile station, fixed or mobilesubscriber unit, pager, or any other type of device capable of operatingin a wireless environment. Such WTRUs include personal communicationdevices, such as phones, video phones, and Internet ready phones thathave network connections. In addition, WTRUs include portable personalcomputing devices, such as PDAs and notebook computers with wirelessmodems that have similar network capabilities. WTRUs that are portableor can otherwise change location are referred to as mobile units.

Typically, a network of base stations is provided wherein each basestation is capable of conducting concurrent wireless communications withappropriately configured WTRUs, as well as multiple appropriatelyconfigured base stations. Some WTRUs may alternatively be configured toconduct wireless communications directly between each other, i.e.,without being relayed through a network via a base station. This iscommonly called peer-to-peer wireless communications. Where a WTRU isconfigured to communicate directly with other WTRUs it may itself alsobe configured as and function as a base station. WTRUs can be configuredfor use in multiple networks, with both network and peer-to-peercommunications capabilities.

One type of wireless system, called a wireless local area network(WLAN), can be configured to conduct wireless communications with WTRUsequipped with WLAN modems that are also able to conduct peer-to-peercommunications with similarly equipped WTRUs. Currently, WLAN modems arebeing integrated into many traditional communicating and computingdevices by manufacturers. For example, cellular phones, personal digitalassistants, and laptop computers are being built with one or more WLANmodems.

Popular WLAN environments with one or more WLAN base stations, typicallycalled access points (APs), include those constructed according to oneor more of the IEEE 802 family of standards. Access to these networksusually requires user authentication procedures. Protocols for suchsystems are presently being standardized in the WLAN technology area.One such framework of protocols is represented by the IEEE 802 family ofstandards.

A basic service set (BSS) is the basic building block of an IEEE 802.11WLAN, which comprises WTRUs also referred to as stations (STAs). A setof STAs which can talk to each other can form a BSS. Multiple BSSs areinterconnected through an architectural component called a distributionsystem (DS), to form an extended service set (ESS). An access point (AP)is a WTRU that provides access to the DS by providing DS services, andgenerally allows concurrent access to the DS by multiple STAs.

A network of WTRUs operating with peer to peer communications in an IEEE802.11 environment, typically referred to as “ad hoc” mode, is alsocalled an “independent BSS.” In an independent BSS, two or more WTRUsestablish communication among themselves without the need of acoordinating network element. No AP-to-network infrastructure isrequired. However, an AP can be configured to use the ad hoc protocolsand act as the WTRUs do in peer to peer communications. In such case anAP may act as a bridge or router to another network or to the Internet.

A WTRU that starts an ad hoc network selects the ad hoc network'soperating parameters, such as the service set identifier (SSID),channel, and beacon timing, and transmits this information incommunication frames, for example, in beacon frames. As other WTRUs jointhe ad hoc network, they detect and use the ad hoc network's operatingparameters.

Where a network infrastructure is used and wireless communications arecontrolled through APs, parameters such as the SSID are normallyspecified by a network controller associated with the APs. The APsperiodically broadcast beacon frames to enable WTRUs to identify the APsand attempt to establish communications with them. For example in FIG.1, a WLAN is illustrated in which WTRUs conduct wireless communicationsvia a network station, in this case an AP. The AP is connected withother network infrastructure such as a Network Management Station (NMS).The AP is shown as conducting communications with five WTRUs. Thecommunications are coordinated and synchronized through the AP.Generally, the WLAN system supports WTRUs with different data rates. Insome cases an AP is configured to support multiple types of WTRUs, suchas 802.11(b) and 802.11(g) compliant WTRUs.

The SSID in an IEEE 802 based system can be a 32-character uniqueidentifier attached to a header of packets sent over a WLAN. The SSIDthen acts as a password when a WTRU attempts to connect to a BSS or anindependent BSS. The SSID differentiates one WLAN from another, so allbase stations and all other devices connected to or attempting toconnect to a specific WLAN normally use the same SSID. A device will notnormally be permitted to join a BSS unless it can provide the correctSSID.

A WLAN system made in accordance with the IEEE 802.11 standard,typically uses a carrier sensing mechanism, where WTRUs sense a wirelessmedium, such as a particular communication channel, before transmittingdata packets to an AP, and only transmit the data packets when themedium is free. If the medium is busy, a WTRU defers its transmission.This works reasonably well when WTRUs are able to receive transmissionsof other WTRUs communicating in the WLAN. However, some WTRUs may behidden from others, and, accordingly, cannot always detect when themedium is busy.

For example, both a first WTRU and a second WTRU may be positioned wherethey are each able to communicate with an AP, but, due to theirlocations, they are not able to communicate with each other. Anobstruction between the two WTRUs, such as a building or a mountain, cancause this situation. When the first WTRU transmits to the AP, thesecond WTRU is not able to sense that the medium is busy due to theobstruction or other cause of lack of communication between the twoWTRUs. If the second WTRU begins to transmit at the same time as thefirst WTRU is, the packets will collide at the AP (i.e., the AP is notable to decode the packets received from both WTRUs at the same time).

In order to reduce the severity or avoid this problem, a NetworkAllocation Vector (NAV) is conventionally used when transmitting on themedium. The NAV provides a timing function that blocks all WTRUs thatreceive it from transmitting during a period of time set by the NAV. TheWTRUs that receive the NAV assume that the medium is busy during theperiod of time equal to the NAV time period. After the NAV period, theWTRUs that had previously received the NAV are free to normally contendfor the medium. Where request to send (RTS) and clear to send (CTS)signaling is used between a WTRU and an AP to grant WTRU requests totransmit data packets, an NAV will be included with the RTS advising allWTRUs in the range of the WTRU transmitting the RTS not to transmit onthe medium. In turn, a CTS response from the AP will include a NAV thatexpires contemporaneously with the NAV in the RTS, thereby alerting allWTRUs receiving the CTS to defer transmissions until the expiration ofthe NAV. The WTRU that sent the RTS and receives a responsive CTStransmits during the NAV period since the CTS overrides the NAV in theCTS for that WTRU. A responsive CTS normally will not be sent inresponse to a WTRU's RTS where that RTS is transmitted during the NAV ofa prior RTS received by the AP.

Various types of antenna systems can be employed by WTRUs. A switchedbeam antenna system is a system where multiple fixed beams are definedand the beam that provides the greatest signal enhancements andinterference reduction is usually selected for conducting acommunication. By using a directional antenna instead of anomni-directional antenna, a higher signal-to-noise ratio (SNR) may beobtained, allowing the link to operate at higher data rates. For basestations, such as APs, the directional beam can also extend thegeographic service area of coverage in the direction of the beam. Thus,a switched beam antenna system may improve the coverage area andtransmission speed due to the gains provided by directional beamsinstead of an omni-directional beam for wireless communications. Using aswitched beam antenna system, an AP can select the best beam to be usedto transmit and receive, depending on the location of a WTRU which isaccessing the AP's network via the AP. The selection can be based on anymetric that reflects an improvement in transmission and/or reception ofthe wireless signals.

Collision problems, such as discussed above, exist irrespective ofwhether a omni-directional or a switched beam antenna system is employedby an AP. For example, consider the case where a first WTRU and a secondWTRU are located at opposite sides of an AP that employs a switched beamantenna system. To send data packets to the first WTRU, the AP activatesa beam pointed toward the first WTRU and starts data packettransmission. At this time, the second WTRU is likely not able to detectthe AP transmission because the beam is pointing toward the first WTRU.Because the second WTRU is unlikely to sense any data traffic, thesecond WTRU could start transmitting at the same time that the AP istransmitting. If the first and second WTRUs are not hidden from eachother, the first WTRU can receive both the second WTRU's transmissionsand the AP's transmission creating a potential collision such that thefirst WTRU would not receive the AP's transmitted data packetssuccessfully.

In order to avoid this problem, before starting to send the data packetsto the first WTRU, the AP can notify all other WTRUs in the AP's servicearea that the medium will be busy. As explained above, this is typicallydone using a NAV. For the AP to reach all WTRUs, the AP can use anomni-directional signal to transmit the NAV information. However, if theAP uses an omni-directional signal to communicate with all WTRUs beforeevery transmission, then the coverage area of the switched beam antennais effectively limited to the area that can be reached by the omnidirectional antenna. Thus, this solution does not extend the coveragearea to the full range of a switched directional antenna system.

“Beam sweeping” has been proposed for switched antenna systems such thatthe antenna beam changes position with time, serving each respectivesector for a period of time. Sectors are visited sequentially, orfollowing some suitable pattern based on the system conditions (systemload, users' positions, etc.). Different methods have been proposed forthe WTRUs to know when to transmit. For example, synchronization betweenthe WTRU and the AP beam sweeping using GPS geolocation or the like.

A characteristic of WLAN systems is that they use beacon signals, whichcontain synchronization information necessary for a WTRU to associatewith a basic service set (BSS). Beacons are transmitted periodically bythe AP to its entire service area, once every beacon period (BP). In asectored service area, the beacons must periodically be transmitted toevery sector within a predetermined time period.

To conserve power, WTRUs may go into a power save mode in betweenbeacons, and only wake up to receive the beacons. If a sector is visitedbefore its beacon period expires, the WTRUs in that sector may be in apower save mode, and any transmissions from the AP will not be received.This situation can be avoided if the beam sweeping pattern is sequentialand the beam is redirected at regular intervals. However, regularsequential beam sweeping does not allow for flexible scheduling of thebeams and, if the sectors are not equally loaded, performance candeteriorate in the more heavily loaded sectors. A variety of irregularsequences are not feasible when a beacon must be transmitted to everysector at the expiration of every beacon period. For example, in a casewhere there are seven sectors, 1-7, a sequence such as1,2,3,4,2,5,6,2,7,1 would not be feasible if the beacon period expiredin the time service started for sector 1 and ended for sector 6, sincesector 7 would not have had a beacon signal sent within the beaconperiod.

It is desirable to provide collision avoidance techniques and equipmentto implement such techniques for beam sweeping systems that facilitate ahigh degree of service flexibility for such systems. The inventors haverecognized that NAV can be used in a beam sweeping system in order toreduce or eliminate the interference that WTRUs from one sector cancause to WTRUs in another sector.

The inventors have also recognized that there are undesirableconsequences associated with a strict NAV collision avoidance approachin a beam sweeping system. Neighboring beams usually have an area ofoverlap. WTRUs that are located in an overlapping area could potentiallybe served by 2 beams, improving their throughput. However, once a WTRUreceives an NAV in one beam, the WTRU defers transmissions for(N−1)*BP/N, and does not transmit in the neighboring beam. Moreover,when a WTRU first turns on and joins a WLAN, the WTRU may join via thebeam that appears first, which might not be the best beam. Also, thesignal strength near the boundary of the beam pattern will beattenuated, and WTRUs near the beam boundary will experience reduceddata rates. Serving WTRUs by more than one beam is desirable tocompensate for the lower data rates.

SUMMARY

A Network Allocation Vector (NAV) approach and a “beam access control”(BAC) technique are provided to address data collision problems in WLANswherein APs provide wireless network access in a service area defined bymultiple sectors via use of a switchable antenna system or the like.Preferably, every time the AP visits a sector and before the AP moves onto the next sector, the AP can set the NAV equal to the time it willtake until its next visit. Alternatively, or in addition, a BAC bit ispreferably transmitted by an AP to control access to the AP by WTRUsdisposed in a service sector in which the BAC is transmitted.

Preferably, when the BAC bit indicates “on”, WTRUs receiving the bit areallowed to transmit and/or contend to transmit on the wireless mediumserving the sector. When the bit is “off”, WTRUs receiving the bit areprohibited from transmitting on the wireless medium until an “on” bit isthereafter received. This mechanism permits APs to dynamically increaseor decrease the time spent in each sector according to the communicationload of the sectors, while reducing or eliminating packet collisionscaused by transmissions from WTRUs which are not in an active sector.

In one aspect of the invention, a selectively configured AP is providedfor a wireless local area network (WLAN). The AP is configured toprovide communication services in a geographic area of service towireless transmit/receive units (WTRUs). A preferred AP includes atransceiver configured to selectively generate directional beams forproviding communication service in sectors of the geographic area ofservice such that each beam provides service to a predefined sectorwhereby collectively the directional beams provide service to the entiregeographic service area. A control unit is operatively associated withthe transceiver and is preferably configured to control the generationof the directional beams by the transceiver to switch from beam to beamsuch that service is provided only during selected periods in eachsector. The preferred configuration of the control unit is such that abeam access control (BAC) signal is transmitted to WTRUs located in asector indicating the cessation of a service period for that sectorbefore switching to another beam to provide service in the sectorassociated with the other beam. Alternatively, or in addition, thecontrol unit is configured such that NAV is transmitted to WTRUs locatedin a sector reflecting the time until service will resume in the sector.

For implementing a WLAN employing such an AP, wireless transmit/receiveunits (WTRUs) are provided that have a transceiver configured to receivesignals transmitted by such an AP when providing service in a sector inwhich the WTRU is then located. Preferably the WTRUs are configured tosuspend transmission of signals to the AP in response to receiving a BACsignal that indicates the cessation of a service period for that sectoruntil receiving a further BAC signal from the AP. Alternatively, or inaddition, the WTRUs are configured to suspend transmission of signals tothe AP until the expiration of a controlling NAV.

In another aspect of the invention the AP has a control unit preferablyconfigured to switch from beam to beam such that service is providedonly during selected service periods (SPs) in each sector during apredefined beacon period (BP). A beacon service period (SP_(beacon)) ispreferably provided for every sector in which to transmit a beaconsignal at least once during each BP. A beam access control (BAC) signalis preferably transmitted within each SP_(beacon) to controltransmissions by WTRUs receiving the BAC signal during the BP.

Other objects and advantages will be apparent to those of ordinary skillin the art based upon the following description of presently preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system overview diagram illustrating conventional wirelesscommunication in a wireless local area network (WLAN).

FIG. 2 is an operational diagram of a WLAN access point (AP) having aswitched beam antenna system that provides antenna beam coverage for aplurality of sectors in accordance with the present invention.

FIG. 3 is a flow diagram of a process for providing wireless serviceusing a switched beam in accordance with the present invention.

DETAILED DESCRIPTION

The invention is particularly useful when used in conjunction withwireless local area networks (WLANs), such as those made in accordancewith the IEEE 802 family of standards where WTRUs sense a wirelessmedium, such as a particular communication channel, before transmittingdata packets and only transmit the data packets when the medium is free.It is particularly useful where such WLANs include base stations, suchas access points (APs), that have switched beam antenna systems thatprovide antenna beam coverage for a plurality of sectors. However,benefits of the invention can be realized in any type of wirelessnetwork where similar problems are encountered.

By way of example, FIG. 2 illustrates an AP 25 of a WLAN that has aswitched beam antenna system. Wireless service provided by the AP 25through use of the switched beam antenna system is selectively providedto WTRUs, such as WTRUs 27, 29, when located in a service area 30 byselectively serving each of a plurality of sectors 32. The sectors 32collectively define the service coverage area 30 for the AP 25. The AP'santenna system uses one or more directional antennas, such as a phasearray antenna, to produce signal beams such that each beam covers onesector. Adjacent sectors preferably have some overlapping area to avoidcoverage gaps within the overall service area 30. Through the use of thedirectional beams, the effective coverage area 30 extends substantiallybeyond the service area 36 that would typically be provided by AP 25 ifAP 25 only utilized an omni-directional antenna.

The AP of FIG. 2 shows the wireless service area 30 divided into sixsectors. However, a six sector area is provided by way of example and isnot a limitation. Where a relatively large number of sectors define theoverall coverage area 30, relatively narrow beams would typically beimplemented.

A Network Allocation Vector (NAV) approach can be selectively used in abeam sweeping system in order to reduce or eliminate the interferencethat WTRUs from one sector can cause to WTRUs in another sector. Everytime the AP visits a sector and before the AP moves on to the nextsector, the AP preferably sets the NAV equal to the time it will takeuntil its next visit. The WTRUs in that sector will not transmit duringthe NAV period, and will not interfere with active WTRUs in othersectors.

For example, in a typical case, “beam sweeping” can be configured sothat each sector is visited successively for a predefined period, with aperiod between the start of one visit and the next equal to the beaconperiod (BP), i.e. the maximum time allowed between the broadcast ofsuccessive beacon signals. For an area with N sectors, the AP serviceseach sector for a period of time equal to BP/N in length. For example,if BP=600 ms and N=6, the AP services in each sector with a directionalbeam for 100 ms each visit. Every time the AP visits a sector, ittypically will initially transmit a beacon signal. During the time theAP is covering a sector, WTRUs disposed in that sector are served atvery high data rates. Note that BP=600 ms is just used for the sake ofillustration, and any value could be used.

Every time the AP visits a sector, before the AP moves on to the nextsector it can set and transmit a NAV equal to (N−1)*BP/N to all WTRUs inthe sector, during which time the WTRUs in that sector assume that themedium is busy. After that time the AP will return to that sector (i.e.,it will point a beam to that sector) and the WTRUs in that sector areagain able to contend for the medium.

Instead of, or in addition to, using a NAV technique for avoiding signalcollisions on the wireless medium, the present invention provides analternative approach which is designed to improve collision prevention,particularly in the switched beam antenna context. The inventionintroduces “beam access control” (BAC) whereby an “on/off” bit,hereinafter referred to as a BAC bit, is broadcast by a base station,such as AP 25, to every sector. The WTRUs 27, 29 that communicate in thenetwork are configured to receive and process the BAC bit in conjunctionwith the control of their respective transmissions as set forth below.All such WTRUs that receive the BAC bit set to “on” are allowed totransmit. All WTRUs that receive the BAC set to “off” must defertransmission until they receive another BAC with the bit set to “on”. Byutilizing this BAC technique in a WLAN, such as an IEEE 802 compliantWLAN, flexibility is improved while beacon periodicity is respected.

Preferably, an “on” BAC bit is broadcast by the AP 25 every time a beamis first directed to a sector and an “off” BAC bit is broadcast by theAP 25 every time the beam is about to be switched to another sector. TheBAC bit can be sent in any other appropriate way, such as, for example,in a beacon frame, in a separate signaling packet designated as reservedfor the BAC bit, or attached to the header of data packets. Thisrelatively simple procedure allows a WTRU to be served by any beam thatserves a sector in which the WTRU is located. Accordingly, when a WTRU,such as WTRU 29, is located in an overlap area covered by differentsectors, that WTRU would receive the BAC bit from beams directed to eachof the sectors that encompass the overlap region.

In this manner, the AP 25 can visit a sector, “turn on”, i.e. allowtransmissions from, all the WTRUs in that sector, send and receive datain that sector, then “turn off”, i.e. block transmissions from, allWTRUs in that sector and move on to the next sector. Stations in areasin which beams overlap may transmit whenever they receive an “on” BAC,regardless of the beam in which it was sent.

Utilization of the BAC technique permits an AP to use load-based orother algorithms to dynamically select the beam switching pattern bestsuited to the location and service requirements of the WTRUs in itsservice area. Utilization of the BAC technique also facilitatescombination of the beam switching pattern with an algorithm in the APfor queuing and scheduling of data packet transmissions. As WTRUsrelocate to different sectors or change their service demands, suchalgorithms enable the AP to change the switching pattern to meet newconditions.

Where the WLAN requires APs to transmit beacon signals at a definedpredetermined interval, i.e. beacon period (BP), it is necessary for anAP to provide service, i.e. direct a beam, to every sector at least onceevery BP. Conventionally, an AP will direct a beam to each successivesector for a period of time, a service period (SP), equal to the beaconperiod divided by the number N of sectors, i.e. SP=BP/N. Utilization ofthe BAC technique, permits an AP to use shorter service periods andreallocate service periods from a fixed sequence. For example, if thereis no traffic in a given sector, after the AP 25 sends the beacon andwaits for some period of time in order to allow for new WTRUs toassociate with the AP, it can then send a BAC “off” to that sector andmove on to serve another sector until it is time to send another beaconto the first sector.

Typically a minimum SP for transmitting a beacon signal, SP_(bpmin), canbe defined that is less than BP/N and provides sufficient time to allowfor new WTRUs, if any, to associate with the AP. Accordingly, toregularly transmit beacon signals in all sectors within a period BP, foran AP serving N sectors, a beacon signal can be sent in a first sectorduring a SP_(bpmin) starting at time T_(o) and in each ith sector duringa SP_(bpmin) starting at time T₀+[(BP/N)*(i−1)mod N]. The time between,for example, the end of the service period providing a beacon signal tothe first sector, T₀+SP_(bpmin), and the time before the beginning ofthe service period providing a beacon signal to the second sector,T₀+(BP/N), can be delegated for serving any other sector. These interimperiods can be divided into multiple SPs of various duration to serveany of the sectors as determined by an appropriate scheduling algorithmimplemented in the AP.

For convenience, a fixed length service period, SP_(fx), can be usedthat is at least as long as the minimum SP for transmitting a beaconsignal, SP_(fx)≧SP_(bpmin), and equally divides the periods between thestart of each required successive beacon transmission, i.e.SP_(fx)=(BP/N)/J where J is an integer greater than 1. For the AP 25 ofFIG. 2 that serves six sectors, an SP_(fx) could be set equal to BP/12so that there are 12 SPs during each BP. Accordingly, within any givensequence of 12 SPs, SP1 through SP12, each odd SP can be allocated forproviding the required beacon signal in the six sectors, respectively,and the even SPs can be allocated based on comparative communicationneeds among the six sectors. Alternatively, the first six SPs, SP1through SP6, can be used for providing the required beacon signal in thesix sectors, respectively, and the last six SPs, SP7 through SP12, canbe allocated based on comparative communication needs among the sixsectors. In the latter case multiple consecutive SPs can be allocated toany of the sectors which can be advantageous to reduce signaling.

As an alternative example, for serving N sectors, for any given periodBP, beacons can be sent to the N respective sectors in N successiveminimum periods, SP_(bpmin), so that there is a time equal toBP−(N*SP_(bpmin)) available for dynamic service allocation among thesectors. In such case, if SP_(bpmin) is relatively very small, a BAC canbe sent in the beacon signals to control the WTRUs for the post-beacondynamically allocated service period of a BP, SP_(postbeacon), duringwhich the AP serves one or more sectors based on a load algorithm.

One manner of operation in this regard is set forth in FIG. 3. Asrepresented by step 41, the AP can make its decision for a next BP whichsector to service for the SP_(postbeacon) which may be divided intomultiple SPs serving different sectors. Then, at the start of that nextBP, at a time T₀, the AP transmits a beacon to every sector from T₀through T₀+(N*SP_(bpmin)). Accordingly, the beacon signal transmissionsstart at time T₀ in a first sector and in a selected order thereafter tothe other sectors. Where such beacon signal transmissions are made, theAP preferably sends a BAC set to “off” in the beacons to all sectorsexcept the sector previously selected to be initially served in the postbeacon period SPs for that BP for which a beacon with the BAC set to“on” is sent as represented in step 43. Thereafter, as reflected in step45, the AP serves the sector selected in step 41.

Where the SP_(postbeacon) is a single SP, the AP serves the same sectoruntil the BP elapses and also decides which sector to serve during thenext BP. Where the SP_(postbeacon) is divided into multiple SPs, at theend of each such sub SP of the SP_(postbeacon), the AP sends a BAC setto “off” and starts in conjunction with making a decision which sectorto serve next, step 41. Where the BP has not elapsed, as reflected instep 47, a beam is directed to the next sector to be served andinitially transmits a BAC set to “on” to that sector. Optionally, duringa BP, all sectors to be served in the SP_(postbeacon) of the next BP canbe identified. Where a fixed SP is used, the AP can readily beconfigured to make such decisions in connection with conventionalscheduling of transmission and receipt of data packets.

If a WTRU is able to receive more than one beacon, such as WTRU 29 whichis located in an area where beams overlap, the WTRU can contend for themedium whenever it receives an “on” BAC from a beam serving eithersector. In the immediately preceding example where the BAC bit is sentin successive SP_(bpminS), the “on” BAC can be sent as a 1 value and“off” BAC is sent as a 0 value. Then the WTRUs can be configured to sumall BAC values received during any given period of time that is(N*SP_(bpmin)) in length and to treat the sum as the BAC value. In thiscase, a WTRU, such as WTRU 29, can receive an “off” BAC from one beamand an “on” BAC from another beam and remain on for one of twooverlapping sectors in which the WTRU is located.

Where there is a need to have a logical separation between sectors, eachsector can have its own sector or beam identity. The beam identity canbe sent together with the BAC. This enables WTRUs to take advantage ofsuch information. For example, a WTRU can decide which command torespect (“on” or “off”) based on the selected sector in lieu of, forexample, summing values or otherwise determining BAC validity where theWTRU is disposed in an overlapping service area. Optionally, every WTRUmay be assigned a beam during association.

WTRUs need not be configured to process every beacon signal sent. WTRUscan, for example, be configured to process only every W-th beacon. Thevalue of W is preferably determined by the AP as part of a schedulingmechanism. The AP is preferably configured to set the value of Windependently for each sector, and can be configured to dynamicallyadjust that value. The value of W can be transmitted together with theBAC and/or the beam identity when a beam identity is used. Preferably,the AP determines W as a function of the number of sectors (N), the loadof the system, the number of WTRUs in each beam, the fading environment,and/or other variable conditions.

For example, in a case where there are only two sectors in the APcoverage area, a first beam and a second beam can be generated toprovide the wireless service. If there is a required BP=100 ms, the APis required to send a beacon every 100 ms to each of the two sectors. Ifmost WTRUs being served are disposed in the second sector and the firstsector is very lightly loaded a decision can be made to primarily servethe second sector. Then, starting at a time T₀ of a BP, the AP sends abeacon in the first sector setting all WTRUs in the first sector to“off” and a beacon in the second sector setting all WTRUs in the secondsector to “on”, and then serves the users in the second sector for theremaining portion of the 100 ms BP.

In lieu of repeating this process for three successive BPs in order toprovide greater service to the second sector, the AP can send the beaconon the first beam in conjunction with a W value, for example, W=3,notifying the WTRUs in the first sector to be inactive for three BPs,i.e. the next W*BP=300 ms. The AP then services the second sector forthose three BPs. This can create a variable beacon period for eachsector that allows for WTRUs in each sector to go into a sleep mode foran adjustable period of time. Optionally, during the period in which theWTRUs in one sector are in such a sleep mode, the AP can continue tosend the regular periodic beacon in all sectors to allow new WTRUs tojoin any of the sectors served by the AP.

In an IEEE 802.11 compliant system, every WTRU typically performsauthentication and association before starting communication with an APof the 802.11 WLAN. This is a time-consuming process. Supporting highlymobile users in a sectored system can be a problem if authentication andassociation are required every time a WTRU moves to a different sector,since the coverage area is small and the antenna beam covers a sectorfor a short period of time. Utilization of the BAC technique facilitatessupport for higher levels of mobility and fast handoffs between sectorswithout the need of authentication or association by making all sectorspart of the same BSS (i.e., have the same BSSID).

Where there is a need to have a logical separation between sectors, eachAP beam or group of beams can be associated with a different APidentity, as though each sector or group of sectors was being served bya different AP. In this case, the WTRUs can be pre-authenticated duringthe scanning process, allowing for faster transitions/handoffs. This canbe implemented by assigning a different BSSID for each sector. However,a WTRU in an overlapping area would not be able to communicate with theAP in both unless it was configured to use two BSSIDs; normally a WTRUconfigured for an 802.11 WLAN is able to associate with only a singleBSS. Thus, as an enhancement for a WLAN where APs use different BSSIDsfor different sectors, WTRUs can be configured to be able to associatewith more than one BSS for contemporaneous communication with a singleAP via more than one sector in order to allow a WTRU to be served bymultiple beams and also minimizing the mobility impact.

In many WLANs, APs are required to be configured to transmit broadcastand multicast messages to all WTRUs in their respective coverage areas,which for APs using a switched antenna system means all sectors. Inorder to support such functionality, an AP is typically configured tobuffer all data packets associated with broadcast/multicast messages,until the AP transmits all packets. This can cause aging issues, sincenew broadcast messages arrive before the old messages are transmitted.By transmitting the broadcast messages in all sectors before discardingthem, the probabilility that every station receives the messageincreases, since the stations are able to receive packets coming frommultiple sectors. This creates redundancy in the transmission.

In a system with N sectors, the AP serves each sector for somepercentage of the total service time which can be designated as a“service ratio”. Where there is an even distribution of traffic in eachsector, the AP's antenna preferably serves each sector, on average,during 1/N of the time so that the “service ratio” for all sectors is1/N in such conditions. In order to maximize efficiency, or maximize the“service ratio”, the AP may employ multiple antennas that are co-locatedwhere each antenna is configured to serve a different set of sectors.For example, if there are two antennas, each contemporaneously servinghalf of N total sectors, N/2 sectors, the preferred “service ratio” forevenly distributed traffic load would be 2/N. This distribution assumesthat the two antennas do not interfere with each other. Utilization ofthe BAC technique facilitates the use of co-located, multiple antennassince the BAC technique enables the service ratio of any of the sectorsserved by any of the antennas to be adjusted based on load criteria. Insuch context, the BAC transmitted by each antenna is preferablyindependently determined based on the service load requirements andconditions in the sectors served by the respective antennas.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention. Moreover,the beam access control can be combined with other algorithms, such asthe packet scheduling algorithm, increasing the fairness of the system.For example, for users that can be served by multiple beams, the AP cancontrol the total number of packets transmitted to that user (so thatuser is not unfairly receiving too much bandwidth). QoS parameters canalso be used to make decisions on beam access control. For example, ifcertain sectors have users with strict delay requirements (such as usersrunning Voice over IP applications), then these sectors can be visitedmore often in order to guarantee the QoS requirements of the VoIPapplication.

Preferably, decision logic circuitry for determining BAC bit values andformatting communication data frames including BAC data for transmissionto WTRUs are implemented on a single integrated circuit for an AP, suchas an application specific integrated circuit (ASIC), with the interfacecomponent and one or more of the components that implement therespective network communication protocol stacks. However, thecomponents may also be readily implemented on multiple separateintegrated circuits. Similarly, WTRU signal processing circuitry thatprocesses received communication frames including BAC data inassociation with controlling the mode of the WTRU are preferablyimplemented on an ASIC.

The foregoing description makes references to specific AP and networkconfigurations as an example only and not as a limitation. Othervariations and modifications consistent with the invention will berecognized by those of ordinary skill in the art.

1. A method implemented in an access point (AP) for wirelesscommunication with at least one wireless transmit/receive unit (WTRU),comprising: transmitting a beacon signal periodically among a pluralityof sectors, each sector having its own sector identity, the beaconsignal being periodically received at least once in a beacon period andthe beacon period comprising a plurality of beacon service periods forall sectors; determining a scheduling value to indicate a number W ofinactive beacon periods for a first sector to at least one WTRU locatedin the first sector; transmitting a beam access control (BAC) signal viaat least one directional beam in a sector in which the first WTRU islocated during a beacon service period, the BAC signal indicatingallowance or disallowance of transmission of a signal from the firstWTRU in the sector during a post-beacon period, the post-beacon periodremaining after the beacon service periods for all sectors; andtransmitting the scheduling value with the sector identity for the firstsector, such that a variable beacon period is established for the firstsector, enabling the at least one WTRU located in the first sector toenter a sleep mode for an adjustable period of time.
 2. The method as inclaim 1, wherein the value W is determined as a function of the numberof sectors.
 3. The method as in claim 1, wherein the value W isdetermined as a function of a load of the AP.
 4. The method as in claim1, wherein the value W is determined as a function of the number ofWTRUs in each sector.
 5. The method as in claim 1, wherein the value Wis determined as a function of a fading environment of the AP.
 6. Themethod as in claim 1 wherein the beam identity is transmitted with theBAC signal.
 7. The method as in claim 1, further comprising: employingmultiple collocated antennas, each antenna configured to serve adifferent set of sectors.
 8. The method as in claim 7, furthercomprising: determining the BAC signal for each antenna independentlybased on service load requirements served by the respective antenna; andadjusting a service ratio of each sector according to the determined BACsignal for each antenna.
 9. The method as in claim 8, wherein the BACsignal is further determined independently based on conditions in thesectors served by the respective antenna.
 10. An access point (AP),configured for wireless communication with at least one wirelesstransmit/receive unit (WTRU), the AP comprising: a transceiverconfigured to transmit a beacon signal periodically among a plurality ofsectors, each sector having its own sector identity, the beacon signalbeing periodically received at least once in a beacon period and thebeacon period comprising a plurality of beacon service periods for allsectors, and further configured to transmit a beam access control (BAC)signal via at least one directional beam in a sector in which the firstWTRU is located during a beacon service period; a control unitconfigured to determine a scheduling value to indicate a number W ofinactive beacon periods for a first sector to at least one WTRU locatedin the first sector, and further configured to determine the BAC signalto indicate allowance or disallowance of transmission of a signal fromthe first WTRU in the sector during a post-beacon period, thepost-beacon period remaining after the beacon service periods for allsectors; and the transceiver configured to transmit the scheduling valuewith the sector identity for the first sector, such that a variablebeacon period is established for the first sector, to enable the atleast one WTRU located in the first sector to enter a sleep mode for anadjustable period of time.
 11. The AP as in claim 10, wherein thecontrol unit is configured to determine the value W as a function of thenumber of sectors.
 12. The AP as in claim 10, wherein the control unitis configured to determine the value W as a function of a load of theAP.
 13. The AP as in claim 10, wherein the control unit is configured todetermine the value W as a function of the number of WTRUs in eachsector.
 14. The AP as in claim 10, wherein the control unit isconfigured to determine the value W as a function of a fadingenvironment of the AP.
 15. The AP as in claim 10 wherein transceiver isconfigured to transmit the beam identity with the BAC signal.
 16. The APas in claim 10, further comprising: multiple collocated antennas, eachantenna configured to serve a different set of sectors.
 17. The AP as inclaim 16, wherein the control unit is configured to determine the BACsignal for each antenna independently based on service load requirementsserved by the respective antenna; and to adjust a service ratio of eachsector according to the determined BAC signal for each antenna.
 18. TheAP as in claim 17, wherein the control unit is further configured todetermine the BAC signal independently based on conditions in thesectors served by the respective antenna.